Wayback Machine: Sun's Rays are Harnessed in Solar Furnace (1924)

You just gotta love Modern Mechanix for finding these things. ARCHIMEDES, famous mathematician, is said to have set fire to the fleet of the Roman emperor, Marcellus, by the use of a series of concave mirrors concentrating the sun’s rays upon the fleet. John Ericsson, the designer of the Monitor, of civil war fame, constructed several engines having boilers provided with mechanical devices for effecting the necessary concentration of solar rays which, when collected from 100 square feet of surface, effected the evaporation of 489 cubic inches of water per hour, more than equivalent to one horsepower. This is, however, but a small proportion of the potential energy actually developed by solar heat hourly received upon an area of this size. Ericsson estimated it to be equivalent to that caused by the combustion of 200 tons of coal in the same time.